Water extracts of Fucus vesiculosus and Laminaria digitata enhance male reproductive parameters via antioxidant and NO/cGMP mechanisms in rats

Male sexual dysfunction is increasingly prevalent, driving interest in marine algal bioactives as potential natural modulators of reproductive physiology. Brown seaweeds such as Fucus vesiculosus and Laminaria digitata contain phlorotannins, fucoidans, and antioxidant compounds of applied relevance in phycology and biotechnology. This study assessed the effects of standardized water extracts of these two species on reproductive behavior, hormonal status, sperm quality, oxidative balance, and nitric oxide (NO)/cyclic guanosine monophosphate (cGMP) signaling in male Sprague–Dawley rats. Animals received the seaweed extracts orally by gavage (300 mg kg⁻1 day⁻1) for 52 days. Both extracts improved male reproductive behavior by reducing the time required to initiate mounting, intromission, and ejaculation (mount latency, intromission latency, and ejaculation latency), while increasing the number of these sexual behaviors during the test period (p < 0.05). Serum follicle-stimulating hormone and testosterone concentrations increased, alongside higher testicular superoxide dismutase, catalase, and glutathione peroxidase activities and lower malondialdehyde levels. Sperm count and motility improved, particularly with L. digitata extract. Western blot analyses revealed phosphorylated phosphodiesterase-5, endothelial NO synthase, and cGMP levels, with reduced endothelin-1 in testicular and epididymal tissues (p < 0.05–0.001). These findings indicate that extracts of F. vesiculosus and L. digitata, chosen for their well-documented antioxidant and phlorotannin-rich profiles, confer protective and prosexual effects associated with enhanced antioxidant defense and upregulation of NO/cGMP-related pathways, with the L. digitata extract exhibiting comparatively stronger activity.